Sources of beams of electromagnetic radiation generally provide intensity vs. wavelength plots which vary with wavelength. In some situations the intensity at one or more wavelengths can be greater than desired as it causes saturation of detector electronics. It is also noted that plots of intensity vs. wavelength have an identifiable “median value”. Where intensity is greater than desired at least one wavelength it can be beneficial to uniformly attenuate said median value over the entire wavelength range in an achromatic manner. That is the attenuation of intensity should be substantially the same at each wavelength. Substantially achromatic intensity attenuation systems are known, such as neutral density filters, but they tend to be expensive. Systems are known which beneficially provide non-achromatic attenuation of beam intensity, such as described in U.S. Pat. No. 7,099,006 to Johs et al. Said 006 Patent teaches that reflecting a beam of electromagnetic radiation off a Silicon substrate which has a layer of SiO2 on the reflective surface thereof attenuates the intensity of visible wavelengths more that UV and IR wavelengths.
A computer Search for Patents describing achromatic attenuation of electromagnetic beam intensity applied in ellipsometers or spectrophotometers provided no Patents. However some Patents which discuss achromatic attenuation of beams were identified and are:
Patent No. 6,169,624 to Godil et al.;
Patent No. 5,223,715 to Taylor; and
Patent No. 5,206,701 to Taylor.
A need exists for a system that is relatively inexpensive but that provides substantially achromatic intensity attenuation over a range of wavelengths.